function Snake(el){
 this.el=el
 this.length=20
 this.snakeObj=[
    { x: 3, y :2, color:'red', el:null}, 
    { x: 2, y :2, color:'blue', el:null},
    { x: 1, y :2, color:'blue', el:null}
  ]
  this.direction="right"
}

//为了让蛇只是变动位置而不是为了加长
Snake.prototype.remove=function(){
    for(let i=0;i<this.snakeObj.length;i++)
    {
        if(this.snakeObj[i].el)//如果存在了的话
        {
         this.el.removeChild(this.snakeObj[i].el)//就移除
        }
    }
}
Snake.prototype.create=function(){
    this.remove()
    for(let i=0;i<this.snakeObj.length;i++)
    {
    let divObj = document.createElement('div')
    divObj.style.width=this.length+"px"
    divObj.style.height=this.length+"px"
    divObj.style.position="absolute"
    divObj.style.left=this.snakeObj[i].x*this.length+"px"
    divObj.style.top=this.snakeObj[i].y*this.length+"px"
    divObj.style.background=this.snakeObj[i].color
    this.snakeObj[i].el=divObj
    this.el.appendChild(divObj)
}
}
Snake.prototype.move=function(){
    for(let i=this.snakeObj.length-1;i>0;i--){
    this.snakeObj[i].x=this.snakeObj[i-1].x
    this.snakeObj[i].y=this.snakeObj[i-1].y
    }
    switch (this.direction) {
        case "top":
            this.snakeObj[0].y-=1
            break;
        case "bottom":
            this.snakeObj[0].y+=1
            break;
        default:
        case "left":
            this.snakeObj[0].x-=1
            break;
        case "right":
            this.snakeObj[0].x+=1
            break;
    }
    this.create()
}